Oro: Experimental Organic Cosmochemistry 471 



particular, were found as intermediates, and formic, lactic, and glycolic acids 

 as side products. 



It was found^'' that the mechanism of synthesis involves the initial formation 

 of formaldoxime and its dehydration into hydrogen cyanide. Strecker and 

 cyanohydrin condensations yield nitriles which are hydrolyzed first into amides 

 and then into acids. Condensation of formaldehyde with glycinamide is 

 presumed to yield serinamide which can be converted into serine and alanine.'"" 

 A similar formation of serine and threonine involving aldol type condensations 

 of formaldehyde and acetaldehyde with methylene-activated glycine deriva- 

 tives, such as glycine chelates or polyglycine, was also shown by Akabori 

 et a/.i"'"i"^ It may be added here that when the formaldehyde-hydroxylamine 

 hydrochloride mixtures were made slightly basic, pyridines were also formed 

 in addition to amino acids. 



A subsequent study in our laboratory of the products formed by refluxing 

 aqueous mixtures of formaldehyde and hydrazine revealed the formation of 

 glycine, vaHne, and lysine as detected by paper chromatography.'"* The 

 mechanism of lysine formation is thought to involve the intermediate formation 

 of hexoses and their reduction-oxidation by hydrazine. It is well known that 

 hexoses are formed from formaldehyde by base catalysis, that hydrazine is 

 formed by the action of electric discharges on ammonia,'"^ and that hydrazines 

 can be both reducing and oxidizing reactants. 



As mentioned earlier, 3 of the major compounds which are supposed to 

 exist in comets are hydrogen cyanide, ammonia, and water. For this reason, a 

 study of the products formed with mixtures of these 3 compounds was subse- 

 quently undertaken in our laboratory. It was observed that the amino acids 

 glycine, alanine, and aspartic acid, and other biochemical compounds were 

 formed spontaneously at moderate temperatures in these mixtures.'*"^ Oli- 

 gomers of hydrogen cyanide are presumed to be the intermediates of the amino 

 acids. In fact, tetrameric hydrogen cyanide was observed to be one of the 

 first products formed in the above mixtures,'"^ and it is known that tetrameric 

 hydrogen cyanide can be hydrolytically degraded into glycine.'"*''"^ Two 

 possible degradation mechanisms of tetrameric hydrogen cyanide into glycine 

 have been suggested by Loquin"" and Ruske."' Other mechanisms involving 

 processes of reductive deamination can be postulated for the formation of 

 alanine and aspartic acid. 



The formation of amino acids in the hydrogen cyanide-ammonia-water 

 mixtures has been confirmed and extended by Lowe et al}^'^ In addition to the 

 above 3 amino acids, Lowe and co-workers have also detected the presence of 

 (8-alanine, a,(8-diaminopropionic, a-aminoisobutyric, glutamic acid, arginine, 

 leucine, and isoleucine in the reaction product. The formation of hydroxy 

 amino acids could conceivably take place in these mixtures if aldehydes were 

 present, because it is known that formaldehyde and acetaldehyde condense 

 with methyleneaminoacetonitrile to form serine and threonine, respectively."^ 



It can thus be seen that, with the exception of the aromatic and sulfur con- 

 taining amino acids, most of the building blocks of proteins can be synthesized 

 nonenzymatically in aqueous sytems from very simple precursors in the absence 

 of highly activating forms of energy. 



